The present system is generally directed to the field of wireless communications. The present system has particular applicability in a wireless access point (AP) or wireless bridge (BR) of the type used in a wireless local area network (WLAN) and employing an antenna system for exchanging wireless signals.
As shown in FIG. 1, a managed wireless local area network (WLAN) 10 includes a network backbone 12, preferably an Ethernet network, and at least one wireless access point (AP) 14 (e.g., AP1, AP2 . . . APN, as indicated). Each access point 14 wirelessly communicates over radio frequencies with a plurality of wireless clients 16. The operation and performance of the wireless local area network 10 is typically handled by a network manager or network management entity (NME) 18. A network manager or network management entity 18 is used to calculate and determine a suitable coverage area that an access point can provide as will be shown and described hereinafter.
Management of an access point is also useful in instances where an access point is used in a stand alone configuration or mode and still needs to meet radiated power limitations imposed by regulation. Use of the present invention allows an access point to maximize output power with a particular antenna while complying with the regulations.
Referring also to FIG. 2, a typical layout for wireless local area network 10 is based on a floor plan 20 of an operating area, e.g. an office or other work area. Each access point 14 has a range, so as to establish a respective coverage area 22 associated with each access point 14. The coverage areas 22 can be selected to cover the anticipated wireless throughput requirements in a given area based on the expected locations of wireless clients within the areas 22. The size of the coverage areas 22 are based on the transmitted power, the antenna gain, and the various obstructions, e.g., metal building components that would interfere with the wireless signals. In the typical management of wireless local area network 10, the access points 14 are configured to transmit at the highest power possible, i.e., powered up to high power, and signals are exchanged. The network manager or network management entity 18 observes the strength of the received signals and uses this information to generate a “path loss vector,” which is an indication of the amount of attenuation in the signal between access points 14. The network manager or network management entity 18 uses this information to calculate the actual range of each access point 14, in order to determine a practical coverage area 22 for each access point 14 that services wireless clients 16 without interfering with other access points. The path loss PL can be determined by the following expression:PL=PRAD−RSSI where
PRAD equals radiated power (measured in dBm); and
RSSI equals a received signal strength indicator (measured in dBm).
The radiated power PRAD itself equals the transmitter power PTx plus the antenna gain GANT so that the path loss can be expressed as:PL=PTx+GANT−RSSI 
However, it can be difficult in practice to isolate these variables and thereby properly establish coverage areas 22. For instance, various access points have different power-output capabilities and different external antennas have different antenna gains. Further, an antenna may be connected to a respective access point using a long coaxial cable. Consequently, there may be a power loss associated with the cable length that complicates the path loss calculation. As a result of these variables, a network manager, e.g., network management entity 18, can only make assumptions about antenna gain from the measured quantities. These factors can also vary across different wireless channels and/or bands, thereby making it difficult to determine suitable coverage areas for a set of access points in a wireless local area network.
In previous systems, the antenna gain is entered manually and the antenna is considered to be an omni-directional antenna. A dipole, for example, is an omni-directional antenna with 2.2 dBi of antenna gain. Other types of omni-directional antenna can provide additional antenna gains, but all share a round radiation pattern when looking at a floor plan or map, such as floor 20 shown in FIG. 2. Either a bad assumption or incorrect knowledge of the antenna gain and/or type will cause invalid results by the network management entity 18 regarding network coverage.
Other types of antennas provide additional gain but with different types of radiation patterns. For example, “Yagi” antennas have higher gain and offer a narrow, long radiation pattern. These are typically used for bridging applications, but are also used here as an example. If an access point were to have a Yagi antenna installed, previous systems would not identify the antenna as such, and would likely assume the Yagi antenna to be a omni-directional antenna having less antenna gain.
Moreover, in previous systems, signal strength is simply measured and reported to the network manager, and only inferences can be made about the antenna gain. This uncertainty in antenna gain contributes to the problems of locating clients within a wireless local area network. In a typical system, the location of a client is based on knowing the relative signal strength of the client at different access points. But if the actual antenna gain is different than that assumed, the values used in the calculations will be different than the actual values, and, thus, the path loss calculation will not be correct, resulting in faulty distance determinations. This results in uncertainty in locating clients, since a client's location can only be estimated within an area of potential locations. Also, since variance in signal strength may be the result of other environmental factors, such as internal reflections from metallic construction elements in the building, this contributes further to the uncertainty.
Additionally, current wireless local area network capabilities create problems from a regulatory standpoint. The Federal Communications Commission (FCC) and other national regulatory agencies worldwide place various restrictions on transmitting radio antennas, such as establishing maximum radiated power limits. For wireless local area network devices, the transmit power is limited to 27 dBm or about 500 milliwatts (mW) without the support of transmit power control (TPC), which is part of the European Union (EU) European Telecommunications Standards Institute (ETSI) Broad Band Radio Access Network (BRAN) regulations. Generally, transmit power control requires that an access point transmit at the lowest power possible. These power limitations are necessary to avoid interference with other sources, particularly military radar, that share the same 5 GHz band with the wireless local area network channels in accordance with the Institute of Electrical and Electronics Engineers (IEEE) 802.11(a) protocol. However, this requirement is easily circumvented since it possible to obtain “off the shelf” external antennas that have higher antenna gains than can permissibly be used with a particular access point. For example, it is possible to operate a 20 dBm antenna with a 17 dBm access point for an illegal output of 37 dBm.
Previous-type solutions are known to the problem of connecting non-compliant antennas to access points. For example, it is known to use a “reverse TNC connector.” This type of connector was originally developed for wireless local area network use as a unique connector that was not readily available, thus preventing non-compliant antennas from being used with wireless local area network products. However, after-market adapters are now available that allow non-compliant antennas to be used.